1. Field of the Invention
The present invention relates to a rotor for small motors, which permits ready functioning of a commutator leg part to each commutator segment end and fitting and connection of a varistor, and a manufacturing method therefor.
2. Description of the Related Art
Connection of each commutator segment and a wound wire end according to the prior art will be described with reference to FIG. 5. FIG. 5 shows a schematic perspective view of the commutator unit of a small motor. In the drawing, reference numeral 11 denotes the shaft of a rotor; 22, a commutator segment; 24, a commutator core; and 26, a commutator leg part. Thus the commutator unit is composed of commutator segments 22 arranged over a resin-made commutator core 24 and commutator leg parts 26, each formed integrally with and at the end of a commutator segment 22 for connecting a wound wire end. FIG. 6 shows a profile of the commutator unit shown in FIG. 5 in a state of being coupled with a wound wire end. The commutator leg part 26, as illustrated, is caused to press down a wound wire end by being bent toward the commutator segment, and is spot-welded.
FIG. 7 shows a varistor alone on its right part and the varistor in a fitted and connected state in the left part. In a small motor having a commutator, when a brush in sliding contact with the commutator passes between commutator segments, an arc is generated, and this arc may jam communication equipment or shorten the useful life of the brush. To solve these problems, fitting a varistor to the rotor of the motor as a spark suppressing element is a known art. An example of such varistor has the shape shown in the right part of FIG. 7. Its overall shape is a doughnut-like disk, and has as many electrodes as the magnetic poles of the rotor, i.e. as many as the commutator segments. Each electrode of this varistor 21 is soldered onto one or another of the commutator leg parts 26. This soldering not only electrically connects the varistor 21 but also is mechanically fixed concentrically with the commutator unit 20.
However, by this conventional connecting and fixing method, as oxidized film is formed over the commutator leg part 26 after wound wire ends are pressed down with the commutator leg part 26 and spot-welded, it is difficult to solder the varistor over them. Therefore, the oxidized film of the soldered portion of the commutator leg part has to be scraped off before the varistor is soldered.
The varistor connecting method according to the prior art also involves the problem of having to use a large quantity of solder because the varistor is mechanically fixed by bridging with solder as shown in FIG. 7.
An object of the present invention, therefore, is to solve these problems and make it possible to assemble the commutator unit and to fit and connect the varistor with remarkable working ease without having to scrape off the oxidized film of the soldered portion of the commutator leg part before soldering the varistor or to bridge the varistor using a large quantity of solder.
Another object of the present invention is to enhance the yield of commutator constituent parts relative to the input of materials, facilitate automation, make possible the choice of the most suitable commutator segment material irrespective of the commutator leg part material and reduce the manufacturing cost.
A rotor for small motors and a manufacturing method therefor according to the invention are such that a plurality of rotor magnetic poles of a salient-pole configuration and a commutator unit are provided on the shaft of the rotor, each of the rotor magnetic poles being composed of a winding around a laminated core and each of both ends of each wound wire being connected to a commutator leg part coupled with a tip of a corresponding commutator segment of the commutator unit. Each of the commutator leg parts comprises a base portion extending outward in a direction substantially normal to the radial direction from the tip of the corresponding commutator segment tip and coupled with the commutator segment tip and a tip portion narrowed stepwise to let the ends of a wound wire be connected. A disk-shaped varistor having a hole at the center is mounted over the base portion of each of the commutator leg parts on the reverse side to the winding in the axial direction of a shaft, and each electrode of the varistor is soldered onto the corresponding base portion.
Further according to the present invention, the commutator leg parts are punched and cut out of a reel-wound flat parent metal sheet and fixed to the commutator segment tips.